TECHNICAL FIELD
[0001] The present invention relates to the field of wireless communications technologies,
and in particular, to a signal clipping processing method and a device.
BACKGROUND
[0002] In a wireless communications system, a base station system includes a baseband unit
(Baseband Unit, BBU) and a remote radio unit (Remote Radio Unit, RRU). A power amplifier
(Power Amplifier, PA) is the most important active device in a remote radio unit of
a radio transmitter, and a function of the power amplifier is to amplify an input
signal. Efficiency of the PA is an important factor that affects costs of a radio
transmitter. However, the PA is not completely ideal. When an amplitude of an input
signal exceeds a linear amplification range of the PA, the PA introduces a non-linear
distortion, that is, a non-linear amplification relationship between an output signal
and the input signal. To ensure linearity of the PA, power back-off needs to be performed
on the input signal, and a value of the power back-off depends on a peak-to-average
ratio of a signal. A peak-to-average ratio is a ratio of a signal peak power to an
average power. For a same PA, because a gain of the PA is constant, a higher output
power indicates higher efficiency of the PA. Therefore, to ensure linearity of the
PA, for a higher peak-to-average ratio of a signal, a higher level of power back-off
needs to be performed, which causes a lower output power. When a peak-to-average ratio
of a signal is decreased, efficiency of the PA may be indirectly improved. Therefore,
a peak-to-average ratio of a signal is an important parameter for the radio transmitter.
[0003] For a communications system that uses a multi-carrier technology (such as orthogonal
frequency division multiplex (Orthogonal Frequency Division Multiplex, OFDM)), a peak-to-average
ratio of a baseband signal is high. A conventional method for decreasing a peak-to-average
ratio of a signal is to use a crest factor reduction (Crest Factor Reduction, CFR)
technology. As shown in FIG. 1, a peak-to-average ratio of an original signal is A
(that is, a value obtained by dividing a peak power by a signal average power), some
signals whose amplitudes are relatively high are located in a non-linear amplification
zone. After a clipping technology is used, a peak-to-average ratio is decreased (as
shown in B in FIG. 1). In this case, all signals are located in a linear amplification
zone. Further, an average power of an input signal may be increased, so that a sum
of the peak power and the gain is still equal to a saturation point, thereby improving
efficiency of the PA. However, the CFR technology increases an error vector magnitude
(Error Vector Magnitude, EVM) of a signal, and an increased EVM indicates that a signal
cannot be easily demodulated at a receive end. That is, the CFR technology decreases
a peak-to-average ratio of a signal at the cost of the EVM. If the EVM is excessively
high, it cannot be ensured that data symbols obtained by using various modulation
schemes can be properly demodulated at a receive end.
[0004] Currently, a widely used PC-CFR (Peak Cancellation CFR) algorithm is an effective
algorithm for decreasing a peak-to-average ratio of a signal. A block diagram of the
algorithm is shown in FIG. 2. A high peak-to-average ratio signal is input; peak detection
is performed on the signal; a peak amplitude and phase information are output to a
peak forming module; and a peak location is output to an allocation module. The peak
forming module outputs a peak forming factor that may be represented as α=(|x|-γ)×exp(jθ).
|x| is an amplitude of a peak signal point, γ is a clipping threshold, and θ is a
phase of the peak signal point. The allocation module allocates a cancellation pulse
generator (Cancellation Pulse Generator, CPG) to a detected peak. The CPG generates
a cancellation pulse, the cancellation pulse is pre-stored, and design of the cancellation
pulse depends on such information as a bandwidth of a signal. A quantity of CPGs may
vary. A sum of products obtained by separately multiplying cancellation pulses corresponding
to multiple peaks by peak forming factors corresponding to all peaks is referred to
as a clipping noise. After the clipping noise is subtracted from the input high peak-to-average
ratio signal that is properly delayed, a signal with a decreased peak-to-average ratio
is output. Generally, after the foregoing iteration is performed for two or three
times, a preset target peak-to-average ratio of an output signal may be obtained.
[0005] In an OFDM system, each resource block (that is, a time-frequency resource that includes
OFDM symbols and subcarriers) may transmit data obtained by using different modulation
schemes. However, the PC-CFR algorithm uses a constant cancellation pulse that has
a consistent amplitude-frequency response on a band. Therefore, after clipping processing
is performed on data obtained by using various modulation schemes, obtained EVMs are
almost the same. For different modulation schemes, a receive end has different EVM
requirements while proper demodulation of data is ensured, and a same EVM is unconducive
to further improving efficiency of the PA.
SUMMARY
[0006] The present invention provides a signal clipping processing method and a device,
so as to meet EVM requirements of different modulation schemes, thereby improving
efficiency of a power amplifier.
[0007] According to a first aspect, a signal clipping processing method is provided, where
the method includes:
performing peak detection on an input signal, so as to obtain amplitude information,
phase information, and location information of a peak signal of the input signal;
obtaining, according to amplitude information and phase information of each peak signal,
a peak forming factor that is corresponding to each peak signal and that is used to
adjust an amplitude and/or a phase of a cancellation pulse sequence corresponding
to the peak signal, and separately outputting, according to location information of
each peak signal, a corresponding cancellation pulse sequence, where the cancellation
pulse sequence is determined according to scheduling information of a baseband unit
BBU, and the scheduling information is used to indicate a modulation scheme used when
each resource block for transmitting the input signal is used to transmit a data symbol;
and
calculating a sum of products of peak forming factors corresponding to all peak signals
and cancellation pulse sequences corresponding to all the peak signals, so as to obtain
a clipping noise, and using a difference between the input signal and the clipping
noise as a signal obtained after clipping processing.
[0008] With reference to the first aspect, in a first possible implementation manner, the
method further includes: performing delay processing on the input signal; and
the using a difference between the input signal and the clipping noise as a signal
obtained after clipping processing includes: using a difference between an input signal
obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
[0009] With reference to the first aspect or the first possible implementation manner of
the first aspect, in a second possible implementation manner, a peak forming factor
corresponding to the peak signal is obtained by using the following formula according
to the amplitude information and the phase information of the peak signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0010] With reference to the first aspect, the first possible implementation manner of the
first aspect, or the second possible implementation manner of the first aspect, in
a third possible implementation manner, determining the cancellation pulse sequence
according to the scheduling information includes:
determining, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol;
determining, according to an order of the modulation scheme used when each resource
block is used to transmit a data symbol, a cancellation pulse sub-sequence corresponding
to each resource block, where a higher order of a modulation scheme used when the
resource block is used to transmit a data symbol indicates a smaller amplitude-frequency
response that is of a cancellation pulse sub-sequence corresponding to the resource
block and that is on a frequency band occupied by the resource block; and
adding up all determined cancellation pulse sub-sequences corresponding to all resource
blocks, so as to obtain the cancellation pulse sequence.
[0011] With reference to the third possible implementation manner of the first aspect, in
a fourth possible implementation manner, determining the cancellation pulse sequence
according to the scheduling information includes:
when the scheduling information changes, redetermining the cancellation pulse sequence
according to updated scheduling information.
[0012] With reference to any one of the first aspect, or the first to the fourth possible
implementation manners of the first aspect, in a fifth possible implementation manner,
the input signal is a baseband signal from the baseband unit BBU, or a signal obtained
after previous clipping processing.
[0013] With reference to any one of the first aspect, or the first to the fifth possible
implementation manners of the first aspect, in a sixth possible implementation manner,
before the performing peak detection on an input signal, the method further includes:
performing upsampling processing on a received input signal, and using a signal obtained
after the upsampling processing as the input signal for performing the peak detection.
[0014] According to a second aspect, a communications device is provided, where the communications
device includes:
a cancellation pulse determining module, configured to: determine, according to scheduling
information of a baseband unit BBU, a cancellation pulse sequence, and send the cancellation
pulse sequence to each cancellation pulse generation module for storing, where the
scheduling information is used to indicate a modulation scheme used when each resource
block for transmitting an input signal is used to transmit a data symbol;
a peak detection module, configured to perform peak detection on the input signal,
so as to obtain amplitude information, phase information, and location information
of a peak signal of the input signal;
a peak forming module, configured to obtain, according to amplitude information and
phase information of each peak signal, a peak forming factor that is corresponding
to each peak signal and that is used to adjust an amplitude and/or a phase of a cancellation
pulse sequence corresponding to the peak signal;
an allocation module, configured to separately send location information of each peak
signal to a corresponding cancellation pulse generation module;
a cancellation pulse generation module, configured to separately output, according
to the location information of each peak signal, a corresponding cancellation pulse
sequence; and
a processing module, configured to: calculate a sum of products of peak forming factors
corresponding to all peak signals and cancellation pulse sequences corresponding to
all the peak signals, so as to obtain a clipping noise; and use a difference between
the input signal and the clipping noise as a signal obtained after clipping processing.
[0015] With reference to the second aspect, in a first possible implementation manner, the
communications device further includes: a delay module, configured to perform delay
processing on the input signal; and
the processing module is specifically configured to use a difference between an input
signal obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
[0016] With reference to the second aspect or the first possible implementation manner of
the second aspect, in a second possible implementation manner, the peak forming module
obtains, by using the following formula, a peak forming factor corresponding to the
peak signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0017] With reference to the second aspect, or the first possible implementation manner
of the second aspect or the second possible implementation manner of the second aspect,
in a third possible implementation manner, the cancellation pulse determining module
is specifically configured to:
determine, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol; determine, according to an
order of the modulation scheme used when each resource block is used to transmit a
data symbol, a cancellation pulse sub-sequence corresponding to each resource block,
where a higher order of a modulation scheme used when the resource block is used to
transmit a data symbol indicates a smaller amplitude-frequency response that is of
a cancellation pulse sub-sequence corresponding to the resource block and that is
on a frequency band occupied by the resource block; and add up all determined cancellation
pulse sub-sequences corresponding to all resource blocks, so as to obtain the cancellation
pulse sequence.
[0018] With reference to the third possible implementation manner of the second aspect,
in a fourth possible implementation manner, the cancellation pulse determining module
is further configured to:
when the scheduling information changes, redetermine the cancellation pulse sequence
according to updated scheduling information, and send the redetermined cancellation
pulse sequence to each cancellation pulse generation module for updating.
[0019] With reference to any one of the second aspect, or the first to the fourth possible
implementation manners of the second aspect, in a fifth possible implementation manner,
the input signal is a baseband signal from the baseband unit BBU, or a signal obtained
after previous clipping processing.
[0020] With reference to any one of the second aspect, or the first to the fifth possible
implementation manners of the second aspect, in a sixth possible implementation manner,
if the communications device is an RRU, the communications device further includes:
an upsampling module that is separately connected to the peak detection module and
the delay module, configured to: perform upsampling processing on a received input
signal, and input a signal obtained after the upsampling processing to the peak detection
module as an input signal of the peak detection module.
[0021] With reference to any one of the second aspect, or the first to the sixth possible
implementation manners of the second aspect, in a seventh possible implementation
manner, if the communications device is the BBU, the processing module is further
configured to send the signal obtained after the clipping processing to an RRU for
performing upsampling processing and intermediate frequency clipping processing.
[0022] According to a third aspect, a communications device is provided, where the communications
device includes:
a transceiver, configured to receive an input signal; and
a processor, configured to: determine a cancellation pulse sequence according to scheduling
information of a BBU, where the scheduling information is used to indicate a modulation
scheme used when each resource block for transmitting an input signal is used to transmit
a data symbol; perform peak detection on the input signal, so as to obtain amplitude
information, phase information, and location information of a peak signal of the input
signal; obtain, according to amplitude information and phase information of each peak
signal, a peak forming factor that is corresponding to each peak signal and that is
used to adjust an amplitude and/or a phase of a cancellation pulse sequence corresponding
to the peak signal; separately send location information of each peak signal to a
corresponding cancellation pulse generator; separately output, according to the location
information of each peak signal, a corresponding cancellation pulse sequence; and
calculate a sum of products of peak forming factors corresponding to all peak signals
and cancellation pulse sequences corresponding to all the peak signals, so as to obtain
a clipping noise, use a difference between the input signal and the clipping noise
as a signal obtained after clipping processing, and output, by using the transceiver,
the signal obtained after the clipping processing.
[0023] With reference to the third aspect, in a first possible implementation manner, the
processor is further configured to perform delay processing on the input signal; and
the processor is specifically configured to use a difference between an input signal
obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
[0024] With reference to the third aspect or the first possible implementation manner of
the third aspect, in a second possible implementation manner, the processor obtains,
by using the following formula, a peak forming factor corresponding to the peak signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0025] With reference to the third aspect, the first possible implementation manner of the
third aspect, or the second possible implementation manner of the third aspect, in
a third possible implementation manner, the processor is specifically configured to:
determine, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol; determine, according to an
order of the modulation scheme used when each resource block is used to transmit a
data symbol, a cancellation pulse sub-sequence corresponding to each resource block,
where a higher order of a modulation scheme used when the resource block is used to
transmit a data symbol indicates a smaller amplitude-frequency response that is of
a cancellation pulse sub-sequence corresponding to the resource block and that is
on a frequency band occupied by the resource block; and add up determined cancellation
pulse sub-sequences corresponding to all resource blocks, so as to obtain the cancellation
pulse sequence.
[0026] With reference to the third possible implementation manner of the third aspect, in
a fourth possible implementation manner, the processor is further configured to: when
the scheduling information changes, redetermine the cancellation pulse sequence according
to updated scheduling information, and send the redetermined cancellation pulse sequence
to each cancellation pulse generation module for updating.
[0027] With reference to any one of the third aspect, or the first to the fourth possible
implementation manners of the third aspect, in a fifth possible implementation manner,
the input signal is a baseband signal from the BBU, or a signal obtained after previous
clipping processing.
[0028] With reference to any one of the third aspect, or the first to the fifth possible
implementation manners of the third aspect, in a sixth possible implementation manner,
if the communications device is an RRU, the processor is further configured to: perform
upsampling processing on a received input signal, and use a signal obtained after
the upsampling processing as the input signal for performing the peak detection.
[0029] With reference to any one of the third aspect, or the first to the sixth possible
implementation manners of the third aspect, in a seventh possible implementation manner,
if the communications device is the BBU, the transceiver is further configured to
send the signal obtained after the clipping processing to an RRU for performing upsampling
processing and intermediate frequency clipping processing.
[0030] In the present invention, a cancellation pulse sequence is determined according to
scheduling information of a BBU, and the scheduling information is used to indicate
a modulation scheme used when each resource block for transmitting an input signal
is used to transmit a data symbol, that is, the cancellation pulse sequence is determined
according to the modulation scheme used when each resource block for transmitting
the input signal is used to transmit a data symbol. In this way, after clipping processing
is performed by using the cancellation pulse sequence, EVM losses of data obtained
by using different modulation schemes are different, so as to meet EVM requirements
of different modulation schemes while proper demodulation of data is ensured. Therefore,
a peak-to-average ratio of a signal obtained after the clipping processing is lower,
thereby further improving efficiency of a power amplifier.
BRIEF DESCRIPTION OF DRAWINGS
[0031]
FIG. 1 is a schematic diagram of an input signal power and an output signal power
in a CFR technology;
FIG. 2 is a schematic diagram of a PC-CFR algorithm;
FIG. 3 is a schematic diagram of a signal clipping processing method according to
an embodiment of the present invention;
FIG. 4A is a schematic diagram of a frequency-domain form of a cancellation pulse
sequence used in an embodiment of the present invention;
FIG. 4B is a schematic diagram of a time-domain form of a cancellation pulse sequence
used in an embodiment of the present invention;
FIG. 5A is a schematic diagram of a frequency-domain form of a cancellation pulse
sequence used in a PC-CFR algorithm;
FIG. 5B is a schematic diagram of a time-domain form of a cancellation pulse sequence
used in a PC-CFR algorithm;
FIG. 6 is a schematic diagram of resource block allocation according to an embodiment
of the present invention;
FIG. 7 is a schematic diagram of a signal peak-to-average ratio obtained by using
a PC-CFR algorithm;
FIG. 8A is a constellation diagram obtained by using a QPSK modulation scheme in a
PC-CFR algorithm;
FIG. 8B is a constellation diagram obtained by using a 16QAM modulation scheme in
a PC-CFR algorithm;
FIG. 8C is a constellation diagram obtained by using a 64QAM modulation scheme in
a PC-CFR algorithm;
FIG. 9 is a schematic diagram of a signal peak-to-average ratio obtained by using
a method according to an embodiment of the present invention;
FIG. 10A is a constellation diagram obtained by using a QPSK modulation scheme in
a method according to an embodiment of the present invention;
FIG. 10B is a constellation diagram obtained by using a 16QAM modulation scheme in
a method according to an embodiment of the present invention;
FIG. 10C is a constellation diagram obtained by using a 64QAM modulation scheme in
a method according to an embodiment of the present invention;
FIG. 11 is a schematic diagram of a first communications device according to an embodiment
of the present invention;
FIG. 12 is a schematic diagram of a second communications device according to an embodiment
of the present invention;
FIG. 13 is a schematic diagram of a third communications device according to an embodiment
of the present invention; and
FIG. 14 is a schematic diagram of a fourth communications device according to an embodiment
of the present invention.
DESCRIPTION OF EMBODIMENTS
[0032] In the embodiments of the present invention, clipping processing is performed according
to scheduling information that is of a baseband unit and that is used to indicate
a modulation scheme used when each resource block for transmitting an input signal
is used to transmit a data symbol. Therefore, a peak-to-average ratio of a signal
obtained after the clipping processing is lower while proper demodulation of data
is ensured, thereby improving efficiency of a power amplifier.
[0033] The following further describes the embodiments of the present invention in detail
with reference to this specification. It should be understood that the embodiments
described herein are merely used to explain the present invention but are not intended
to limit the present invention.
[0034] As shown in FIG. 3, a clipping processing method provided in an embodiment of the
present invention includes:
S31. Perform peak detection on an input signal, so as to obtain amplitude information,
phase information, and location information of a peak signal of the input signal.
S32. Obtain, according to amplitude information and phase information of each peak
signal, a peak forming factor that is corresponding to each peak signal and that is
used to adjust an amplitude and/or a phase of a cancellation pulse sequence corresponding
to the peak signal, and separately output, according to location information of each
peak signal, a corresponding cancellation pulse sequence, where the cancellation pulse
sequence is determined according to scheduling information of a BBU, and the scheduling
information is used to indicate a modulation scheme used when each resource block
for transmitting the input signal is used to transmit a data symbol.
S33. Calculate a sum of products of peak forming factors corresponding to all peak
signals and cancellation pulse sequences corresponding to all the peak signals, so
as to obtain a clipping noise; and use a difference between the input signal and the
clipping noise as a signal obtained after clipping processing.
[0035] In the method provided in this embodiment of the present invention, a cancellation
pulse sequence is determined according to scheduling information of a BBU, and the
scheduling information is used to indicate a modulation scheme used when each resource
block for transmitting an input signal is used to transmit a data symbol, that is,
the cancellation pulse sequence is determined according to the modulation scheme used
when each resource block for transmitting the input signal is used to transmit a data
symbol. In this way, after clipping processing is performed by using the cancellation
pulse sequence, EVM losses of data obtained by using different modulation schemes
are different, so as to meet EVM requirements of different modulation schemes while
proper demodulation of data is ensured. Therefore, a peak-to-average ratio of a signal
obtained after the clipping processing is lower, thereby further improving efficiency
of a power amplifier.
[0036] In this embodiment, the foregoing step S31 to step S33 are an iteration process.
Generally, after the iteration process is performed for two or three times, a preset
target peak-to-average ratio of an output signal may be obtained. If clipping processing
is performed for the first time, the input signal of the foregoing step S31 to step
S33 is a baseband signal from the BBU; or if clipping processing is performed for
the second time or a subsequent time, the input signal of the foregoing step S31 to
step S33 is a signal obtained after previous clipping processing.
[0037] In this embodiment, the foregoing step S31 to step S33 may be implemented in a remote
radio unit or may be implemented in a baseband unit.
[0038] Scheduling information involved in this embodiment of the present invention includes
a modulation scheme used when each resource block for transmitting the input signal
is used to transmit a data symbol. As an implementation manner, the scheduling information
may be represented by using bit information. For example, every two bits represent
a modulation scheme used when a resource block is used to transmit a data symbol:
"00" represents reservation, "01" represents that a modulation scheme used when the
resource block is used to transmit a data symbol is quadrature phase shift keying
(Quadrature Phase Shift Keying, QPSK), "10" represents that a modulation scheme used
when the resource block is used to transmit a data symbol is 16 quadrature amplitude
modulation (16 Quadrature Amplitude Modulation, 16QAM), and "11" represents that a
modulation scheme used when the resource block is used to transmit a data symbol is
64QAM. It is assumed that a modulation scheme used when resource blocks 1 to 7 are
used to transmit a data symbol is a QPSK modulation scheme, a modulation scheme used
when resource blocks 8 to 13 are used to transmit a data symbol is a 16QAM modulation
scheme, and a modulation scheme used when resource blocks 14 to 20 are used to transmit
a data symbol is a 64QAM modulation scheme, 40-bit signaling may be used to represent
scheduling information, and is specifically: 0101010101010110101010101011111111111111.
[0039] In this embodiment, if the foregoing step S31 to step S33 are implemented in the
remote radio unit, the scheduling information needs to be obtained from the baseband
unit by interacting with the baseband unit; or if the foregoing step S31 to step S33
are implemented in the baseband unit, the scheduling information may be directly obtained.
[0040] Based on any one of the foregoing embodiments, in step S31, by means of the peak
detection performed on the input signal, one peak signal may be detected, or two or
more peak signals may be detected.
[0041] Correspondingly, if, in step S31, multiple peak signals are detected, and amplitude
information, phase information, and location information of multiple peak signals
are obtained, in step S32, for all peak signals detected in step S31, corresponding
peak forming factors may be obtained, and cancellation pulse sequences corresponding
to all peak signals are separately output. Alternatively, for some peak signals detected
in step S31, corresponding peak forming factors may be obtained, and cancellation
pulse sequences corresponding to all of the some peak signals are separately output.
[0042] In this embodiment, in step S32, the peak forming factor that is corresponding to
each peak signal and that is used to adjust an amplitude and/or a phase of a cancellation
pulse sequence corresponding to the peak signal is obtained by using the following
formula according to the amplitude information and the phase information of the peak
signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0043] Specifically, the peak forming factor that is corresponding to the peak signal obtained
in step S32 is a complex number. The amplitude and/or the phase of a maximum sampling
point of the cancellation pulse sequence corresponding to the peak signal may be adjusted
according to the peak forming factor, for example, to perform amplitude scaling, so
that an amplitude and a phase of a maximum sampling point of the cancellation pulse
sequence are the same as an amplitude and a phase of a peak signal corresponding to
the cancellation pulse sequence.
[0044] In this embodiment, determining the cancellation pulse sequence according to the
scheduling information includes:
determining, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol;
determining, according to an order of the modulation scheme used when each resource
block is used to transmit a data symbol, a cancellation pulse sub-sequence corresponding
to each resource block, where a higher order of a modulation scheme used when the
resource block is used to transmit a data symbol indicates a smaller amplitude-frequency
response that is of a cancellation pulse sub-sequence corresponding to the resource
block and that is on a frequency band occupied by the resource block; and
adding up determined cancellation pulse sub-sequences corresponding to all resource
blocks, so as to obtain the cancellation pulse sequence.
[0045] Specifically, when a cancellation pulse sequence is designed, for a resource block
that carries a data symbol obtained by using a high-order modulation scheme (for example,
64QAM), an amplitude-frequency response that is of a cancellation pulse sub-sequence
corresponding to the resource block and that is on a frequency band occupied by the
resource block is relatively small. On the contrary, for a resource block that carries
a data symbol obtained by using a low-order modulation scheme (for example, QPSK),
an amplitude-frequency response that is of a cancellation pulse sub-sequence corresponding
to the resource block and that is on a frequency band occupied by the resource block
is relatively large. In this embodiment of the present invention, a method for determining
cancellation pulse sequence has relatively low impact on data obtained by using the
high-order modulation scheme and has relatively high impact on data obtained by using
the low-order modulation scheme. Therefore, not only data obtained by using different
modulation schemes can be properly demodulated at a receive end, but a peak-to-average
ratio of an output signal is lower.
[0046] For example, it is assumed that data carried by a signal bandwidth of 18 MHz is separately
modulated by using QPSK, 16QAM, and 64QAM. When a cancellation pulse sequence is designed,
an amplitude-frequency response that is of a cancellation pulse sub-sequence corresponding
to data obtained by using the QPSK and that is on a frequency band occupied by a resource
block that carries the data is the largest; an amplitude-frequency response that is
of a cancellation pulse sub-sequence corresponding to data obtained by using the 16QAM
and that is on a frequency band occupied by a resource block that carries the data
is the second largest; and an amplitude-frequency response that is of a cancellation
pulse sub-sequence corresponding to data obtained by using the 64QAM and that is on
a frequency band occupied by a resource block that carries the data is the smallest.
A frequency-domain form of the designed cancellation pulse sequence is shown in FIG.
4A, and a time-domain form of the designed cancellation pulse sequence is shown in
FIG. 4B. Compared with a frequency-domain form (as shown in FIG. 5A) and a time-domain
form (as shown in FIG. 5B) of an existing PC-CFR cancellation pulse sequence, in a
frequency domain, amplitude-frequency responses of cancellation pulse sequences in
a signal bandwidth are different, and in a time domain, a cancellation pulse sequence
is a series of complex values.
[0047] Preferably, a specific value of a cancellation pulse sequence may be configured in
proportion according to target EVM values of different modulation schemes. For example,
it is assumed that data carried by a signal bandwidth of 18 MHz is separately modulated
by using QPSK, 16QAM, and 64QAM. When proportional configuration is performed, an
amplitude-frequency response that is of a cancellation pulse sub-sequence corresponding
to data obtained by using QPSK and that is on a frequency band occupied by a resource
block that carries the data is the largest; an amplitude-frequency response that is
of a cancellation pulse sub-sequence corresponding to data obtained by using 16QAM
and that is on a frequency band occupied by a resource block that carries the data
is the second largest; and an amplitude-frequency response that is of a cancellation
pulse sub-sequence corresponding to data obtained by using 64QAM and that is on a
frequency band occupied by a resource block that carries the data is the smallest.
Therefore, amplitude-frequency responses of all cancelltion pulse sub-sequences of
cancellation pulse sequences may be configured to 1.5:1:0.5.
[0048] Based on any one of the foregoing embodiments, in this embodiment, because a modulation
scheme used when each resource block is used to transmit a data symbol changes, scheduling
information that is used to indicate a modulation scheme used when each resource block
for transmitting the input signal is used to transmit a data symbol changes accordingly;
and determining the cancellation pulse sequence according to the scheduling information
includes:
when the scheduling information changes, redetermining the cancellation pulse sequence
according to updated scheduling information.
[0049] Based on any one of the foregoing embodiments, in this embodiment, if the foregoing
step S31 to step S33 are implemented in the remote radio unit, before S31, the method
further includes:
performing upsampling processing on a received input signal, and using a signal obtained
after the upsampling processing as the input signal for performing the peak detection.
[0050] Specifically, if upsampling is performed on an input signal by using an upsampling
multiple of 5, a digital intermediate frequency signal is output. That is, four 0s
are inserted between two sampling points, and a result obtained thereof is sent to
a low-pass finite impulse response (Finite Impulse Response, FIR) filter. A passband
of the filter is 10 MHz, a stopband of the filter is 20.72 MHz, and a sampling rate
of the filter is 153.6 MHz. Certainly, this embodiment of the present invention is
not limited to using an upsampling multiple of 5, and another upsampling multiple
may also be used. However, if the upsampling multiple is excessively small, for a
radio frequency signal obtained after clipping, peak regrowth occurs. If the upsampling
multiple is excessively large, complexity of clipping processing is improved. In this
embodiment of the present invention, before clipping processing is performed, upsampling
processing is first performed on an input signal, so as to avoid peak regrowth of
a radio frequency signal obtained after clipping.
[0051] In the following, a result obtained after clipping processing is performed by using
the method provided in this embodiment of the present invention is compared with a
result obtained after clipping processing is performed by using the existing PC-CFR
algorithm. Details are as follows:
[0052] It is assumed that a baseband signal from the baseband unit is a Long Term Evolution
(Long Term Evolution, LTE) signal of 20 MHz. A baseband signal of an
lth OFDM symbol is represented as:

where
ak,l represents a to-be-transmitted data symbol carried on a subcarrier, where each subcarrier
carries a data symbol, and there are a total of 1200 subcarriers; □
f represents a subcarrier interval (which is 15 KHz in this embodiment);
Ncp,l represents a quantity of cyclic prefix sampling points;
Ts = 1/
fs represents sampling time (
fs = 30.72MHz in this embodiment); and k represents a subcarrier number whose value
range is [-600 600].
[0053] An actual signal bandwidth is 18 MHz. It is assumed that a bandwidth of a resource
block that can be scheduled is 900 KHz, to-be-transmitted data symbols in a same resource
block use a same modulation scheme, and a scheduling period is 1 ms. In each scheduling
period, a quantity of resource blocks is 20. As shown in FIG. 6, a bandwidth is divided
into three consecutive parts. Bandwidths of all the parts are respectively 6.3 MHz,
5.4 MHz, and 6.3 MHz, and respectively include 7, 6, and 7 resource blocks. The three
parts are respectively used to transmit data symbols obtained by using QPSK, 16QAM,
and 64QAM.
[0054] It is assumed that a target peak-to-average ratio is set to 7 dB. After iteration
based on a PC-CFR algorithm is performed three times, a peak-to-average ratio of a
signal is decreased from 9.62 dB to 7.06 dB, as shown in FIG. 7, and a preset target
is met. From a perspective of EVM, for a symbol modulated by using QPSK, it can be
learned from a constellation diagram shown in FIG. 8A that an obtained EVM is 4.89%;
for a symbol modulated by using 16QAM, it can be learned from a constellation diagram
shown in FIG. 8B that an obtained EVM is 4.65%; and for a symbol modulated by using
64QAM, it can be learned from a constellation diagram shown in FIG. 8C that an obtained
EVM is 4.97%. In this case, it can be learned from the constellation diagrams that
data symbols modulated by using the QPSK and the 16QAM can be easily demodulated.
EVMs required by the QPSK and the 16QAM are respectively less than 12.5% and less
than 17.5%. This indicates that a peak-to-average ratio of a signal can be further
decreased.
[0055] It is assumed that a target peak-to-average ratio is set to 6 dB. After iteration
is performed for three times by using the method provided in this embodiment of the
present invention, a peak-to-average ratio is decreased from 9.62 dB to 6.18 dB, as
shown in FIG. 9. From a perspective of EVM, for an output signal, an obtained EVM
of a data symbol modulated by using 64QAM is 4.54% (as shown in a constellation diagram
in FIG. 10A); an obtained EVM of a data symbol modulated by using 16QAM is 8.61% (as
shown in a constellation diagram in FIG. 10B); and an obtained EVM of a data symbol
modulated by using QPSK is 11.92% (as shown in a constellation diagram in FIG. 10C).
In this case, it can be learned from the constellation diagrams that after clipping
processing is performed by using the method provided in this embodiment of the present
invention, EVMs of data symbols modulated by using the QPSK, the 16QAM, and the 64QAM
are different, but the data symbols may be properly demodulated. It can be learned
that, by using the method provided in this embodiment of the present invention, a
peak-to-average ratio of a signal is further decreased while proper demodulation of
a data symbol is ensured.
[0056] Based on a same invention concept, an embodiment of the present invention further
provides a communications device. As shown in FIG. 11, the communications device includes:
a cancellation pulse determining module 111, configured to: determine, according to
scheduling information of a BBU, a cancellation pulse sequence, and send the cancellation
pulse sequence to each cancellation pulse generation module 112 for storing, where
the scheduling information is used to indicate a modulation scheme used when each
resource block for transmitting an input signal is used to transmit a data symbol;
a peak detection module 113, configured to perform peak detection on the input signal,
so as to obtain amplitude information, phase information, and location information
of a peak signal of the input signal;
a peak forming module 114, configured to obtain, according to amplitude information
and phase information of each peak signal, a peak forming factor that is corresponding
to each peak signal and that is used to adjust an amplitude and/or a phase of a cancellation
pulse sequence corresponding to the peak signal;
an allocation module 115, configured to separately send location information of each
peak signal to a corresponding cancellation pulse generation module;
a cancellation pulse generation module 112, configured to separately output, according
to the location information of each peak signal, a corresponding cancellation pulse
sequence; and
a processing module 116, configured to: calculate a sum of products of peak forming
factors corresponding to all peak signals and cancellation pulse sequences corresponding
to all the peak signals, so as to obtain a clipping noise; and use a difference between
the input signal and the clipping noise as a signal obtained after clipping processing.
[0057] According to the communications device provided in this embodiment of the present
invention, a cancellation pulse sequence is determined according to scheduling information
of a BBU, and the scheduling information is used to indicate a modulation scheme used
when each resource block for transmitting an input signal is used to transmit a data
symbol, that is, the cancellation pulse sequence is determined according to the modulation
scheme used when each resource block for transmitting the input signal is used to
transmit a data symbol. In this way, after clipping processing is performed by using
the cancellation pulse sequence, EVM losses of data obtained by using different modulation
schemes are different, so as to meet EVM requirements of different modulation schemes
while proper demodulation of data is ensured. Therefore, a peak-to-average ratio of
a signal obtained after the clipping processing is lower, thereby further improving
efficiency of a power amplifier.
[0058] In this embodiment, the communications device further includes: a delay module 117,
configured to perform delay processing on the input signal; and
the processing module 116 is specifically configured to use a difference between an
input signal obtained after the delay processing and the clipping noise as the signal
obtained after the clipping processing.
[0059] In this embodiment, the peak forming module 114 obtains, by using the following formula,
a peak forming factor corresponding to the peak signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0060] Based on any one of the foregoing embodiments, the cancellation pulse determining
module 111 is specifically configured to:
determine, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol; determine, according to an
order of the modulation scheme used when each resource block is used to transmit a
data symbol, a cancellation pulse sub-sequence corresponding to each resource block,
where a higher order of a modulation scheme used when the resource block is used to
transmit a data symbol indicates a smaller amplitude-frequency response that is of
a cancellation pulse sub-sequence corresponding to the resource block and that is
on a frequency band occupied by the resource block; and add up determined cancellation
pulse sub-sequences corresponding to all resource blocks, so as to obtain the cancellation
pulse sequence.
[0061] Further, the cancellation pulse determining module 111 is further configured to:
when the scheduling information changes, redetermine the cancellation pulse sequence
according to updated scheduling information, and send the redetermined cancellation
pulse sequence to each cancellation pulse generation module for updating.
[0062] Based on any one of the foregoing embodiments, if clipping processing is performed
for the first time, the input signal is a baseband signal from the BBU; or if clipping
processing is performed for the second time or a subsequent time, the input signal
is a signal obtained after previous clipping processing.
[0063] Based on any one of the foregoing embodiments, if the communications device is an
RRU, as shown in FIG. 12, the communications device further includes:
an upsampling module 118 that is connected to the peak detection module 113, configured
to: perform upsampling processing on a received input signal, and input a signal obtained
after the upsampling processing to the peak detection module 113 as an input signal
of the peak detection module 113.
[0064] Based on any one of the foregoing embodiments, if the communications device is the
BBU, as shown in FIG. 13, the processing module 116 is further configured to send
the signal obtained after the clipping processing to an RRU for performing upsampling
processing and intermediate frequency clipping processing.
[0065] It should be noted that functions of all modules in the foregoing communications
devices provided in this embodiment of the present invention may be implemented by
using specific design of a circuit.
[0066] Based on a same invention concept, an embodiment of the present invention further
provides a communications device. As shown in FIG. 14, the communications device includes:
a transceiver 141, configured to receive an input signal; and
a processor 142, configured to: determine a cancellation pulse sequence according
to scheduling information of a BBU, where the scheduling information is used to indicate
a modulation scheme used when each resource block for transmitting an input signal
is used to transmit a data symbol; perform peak detection on the input signal, so
as to obtain amplitude information, phase information, and location information of
a peak signal of the input signal; obtain, according to amplitude information and
phase information of each peak signal, a peak forming factor that is corresponding
to each peak signal and that is used to adjust an amplitude and/or a phase of a cancellation
pulse sequence corresponding to the peak signal; separately send location information
of each peak signal to a corresponding cancellation pulse generator; separately output,
according to the location information of each peak signal, a corresponding cancellation
pulse sequence; and calculate a sum of products of peak forming factors corresponding
to all peak signals and cancellation pulse sequences corresponding to all the peak
signals, so as to obtain a clipping noise, use a difference between the input signal
and the clipping noise as a signal obtained after clipping processing, and output,
by using the transceiver 141, the signal obtained after the clipping processing.
[0067] In this embodiment, the processor 142 is further configured to perform delay processing
on the input signal; and
the processor 142 is specifically configured to use a difference between an input
signal obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
[0068] In this embodiment, the processor 142 obtains, by using the following formula, a
peak forming factor corresponding to the peak signal:

where α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
[0069] Based on any one of the foregoing embodiments, the processor 142 is specifically
configured to:
determine, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol; determine, according to an
order of the modulation scheme used when each resource block is used to transmit a
data symbol, a cancellation pulse sub-sequence corresponding to each resource block,
where a higher order of a modulation scheme used when the resource block is used to
transmit a data symbol indicates a smaller amplitude-frequency response that is of
a cancellation pulse sub-sequence corresponding to the resource block and that is
on a frequency band occupied by the resource block; and add up determined cancellation
pulse sub-sequences corresponding to all resource blocks, so as to obtain the cancellation
pulse sequence.
[0070] Further, the processor 142 is configured to:
when the scheduling information changes, redetermine the cancellation pulse sequence
according to updated scheduling information, and send the redetermined cancellation
pulse sequence to each cancellation pulse generation module for updating.
[0071] Based on any one of the foregoing embodiments, if clipping processing is performed
for the first time, the input signal is a baseband signal from the BBU; or if clipping
processing is performed for the second time or a subsequent time, the input signal
is a signal obtained after previous clipping processing.
[0072] Based on any one of the foregoing embodiments, if the communications device is an
RRU, the processor 142 is further configured to:
perform upsampling processing on a received input signal, and use a signal obtained
after the upsampling processing as the input signal for performing the peak detection.
[0073] Based on any one of the foregoing embodiments, if the communications device is the
BBU, the transceiver 141 is further configured to:
send the signal obtained after the clipping processing to an RRU for performing upsampling
processing and intermediate frequency clipping processing.
[0074] A person skilled in the art should understand that the embodiments of the present
invention may be provided as a method, a system, or a computer program product. Therefore,
the present invention may use a form of hardware only embodiments, software only embodiments,
or embodiments with a combination of software and hardware. In addition, the present
invention may use a form of a computer program product that is implemented on one
or more computer-usable storage media (including but not limited to a disk memory,
a CD-ROM, an optical memory, and the like) that include computer-usable program code.
[0075] The present invention is described with reference to the flowcharts and/or block
diagrams of the method, the device (system), and the computer program product according
to the embodiments of the present invention. It should be understood that computer
program instructions may be used to implement each process and/or each block in the
flowcharts and/or the block diagrams and a combination of a process and/or a block
in the flowcharts and/or the block diagrams. These computer program instructions may
be provided for a general-purpose computer, a dedicated computer, an embedded processor,
or a processor of any other programmable data processing device to generate a machine,
so that the instructions executed by a computer or a processor of any other programmable
data processing device generate an apparatus for implementing a specific function
in one or more processes in the flowcharts and/or in one or more blocks in the block
diagrams.
[0076] These computer program instructions may be stored in a computer readable memory that
can instruct the computer or any other programmable data processing device to work
in a specific manner, so that the instructions stored in the computer readable memory
generate an artifact that includes an instruction apparatus. The instruction apparatus
implements a specific function in one or more processes in the flowcharts and/or in
one or more blocks in the block diagrams.
[0077] These computer program instructions may be loaded onto a computer or another programmable
data processing device, so that a series of operations and steps are performed on
the computer or the another programmable device, thereby generating computer-implemented
processing. Therefore, the instructions executed on the computer or the another programmable
device provide steps for implementing a specific function in one or more processes
in the flowcharts and/or in one or more blocks in the block diagrams.
[0078] Although some embodiments of the present invention have been described, persons skilled
in the art can make changes and modifications to these embodiments once they learn
the basic inventive concept. Therefore, the following claims are intended to be construed
as to cover the embodiments and all changes and modifications falling within the scope
of the present invention.
[0079] Obviously, a person skilled in the art can make various modifications and variations
to the present invention without departing from the scope of the present invention.
The present invention is intended to cover these modifications and variations provided
that they fall within the scope of protection defined by the following claims and
their equivalent technologies.
1. A signal clipping processing method, wherein the method comprises:
performing peak detection on an input signal, so as to obtain amplitude information,
phase information, and location information of a peak signal of the input signal;
obtaining, according to amplitude information and phase information of each peak signal,
a peak forming factor that is corresponding to each peak signal and that is used to
adjust an amplitude and/or a phase of a cancellation pulse sequence corresponding
to the peak signal, and separately outputting, according to location information of
each peak signal, a corresponding cancellation pulse sequence, wherein the cancellation
pulse sequence is determined according to scheduling information of a baseband unit
BBU, and the scheduling information is used to indicate a modulation scheme used when
each resource block for transmitting the input signal is used to transmit a data symbol;
and
calculating a sum of products of peak forming factors corresponding to all peak signals
and cancellation pulse sequences corresponding to all the peak signals, so as to obtain
a clipping noise, and using a difference between the input signal and the clipping
noise as a signal obtained after clipping processing.
2. The method according to claim 1, wherein the method further comprises: performing
delay processing on the input signal; and
the using a difference between the input signal and the clipping noise as a signal
obtained after clipping processing comprises: using a difference between an input
signal obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
3. The method according to claim 1 or 2, a peak forming factor corresponding to the peak
signal is obtained by using the following formula according to the amplitude information
and the phase information of the peak signal:

wherein α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
4. The method according to any one of claims 1 to 3, wherein determining the cancellation
pulse sequence according to the scheduling information comprises:
determining, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol;
determining, according to an order of the modulation scheme used when each resource
block is used to transmit a data symbol, a cancellation pulse sub-sequence corresponding
to each resource block, wherein a higher order of a modulation scheme used when the
resource block is used to transmit a data symbol indicates a smaller amplitude-frequency
response that is of a cancellation pulse sub-sequence corresponding to the resource
block and that is on a frequency band occupied by the resource block; and
adding up determined cancellation pulse sub-sequences corresponding to all resource
blocks, so as to obtain the cancellation pulse sequence.
5. The method according to claim 4, wherein determining the cancellation pulse sequence
according to the scheduling information comprises:
when the scheduling information changes, redetermining the cancellation pulse sequence
according to updated scheduling information.
6. The method according to any one of claims 1 to 5, wherein the input signal is a baseband
signal from the baseband unit BBU, or a signal obtained after previous clipping processing.
7. The method according to any one of claims 1 to 6, before the performing peak detection
on an input signal, the method further comprises:
performing upsampling processing on a received input signal, and using a signal obtained
after the upsampling processing as the input signal for performing the peak detection.
8. A communications device, wherein the communications device comprises:
a cancellation pulse determining module, configured to: determine, according to scheduling
information of a baseband unit BBU, a cancellation pulse sequence, and send the cancellation
pulse sequence to each cancellation pulse generation module for storing, wherein the
scheduling information is used to indicate a modulation scheme used when each resource
block for transmitting an input signal is used to transmit a data symbol;
a peak detection module, configured to perform peak detection on the input signal,
so as to obtain amplitude information, phase information, and location information
of a peak signal of the input signal;
a peak forming module, configured to obtain, according to amplitude information and
phase information of each peak signal, a peak forming factor that is corresponding
to each peak signal and that is used to adjust an amplitude and/or a phase of a cancellation
pulse sequence corresponding to the peak signal;
an allocation module, configured to separately send location information of each peak
signal to a corresponding cancellation pulse generation module;
a cancellation pulse generation module, configured to separately output, according
to the location information of each peak signal, a corresponding cancellation pulse
sequence; and
a processing module, configured to: calculate a sum of products of peak forming factors
corresponding to all peak signals and cancellation pulse sequences corresponding to
all the peak signals, so as to obtain a clipping noise; and use a difference between
the input signal and the clipping noise as a signal obtained after clipping processing.
9. The communications device according to claim 8, wherein the communications device
further comprises: a delay module, configured to perform delay processing on the input
signal; and
the processing module is specifically configured to use a difference between an input
signal obtained after the delay processing and the clipping noise as the signal obtained
after the clipping processing.
10. The communications device according to claim 8 or 9, wherein the peak forming module
obtains, by using the following formula, a peak forming factor corresponding to the
peak signal:

wherein α is the peak forming factor, |x| is the amplitude information of the peak
signal, γ is a set clipping threshold, and θ is the phase information of the peak
signal.
11. The communications device according to any one of claims 8 to 10, wherein the cancellation
pulse determining module is specifically configured to:
determine, according to the scheduling information, a modulation scheme used when
each resource block is used to transmit a data symbol; determine, according to an
order of the modulation scheme used when each resource block is used to transmit a
data symbol, a cancellation pulse sub-sequence corresponding to each resource block,
wherein a higher order of a modulation scheme used when the resource block is used
to transmit a data symbol indicates a smaller amplitude-frequency response that is
of a cancellation pulse sub-sequence corresponding to the resource block and that
is on a frequency band occupied by the resource block; and add up determined cancellation
pulse sub-sequences corresponding to all resource blocks, so as to obtain the cancellation
pulse sequence.
12. The communications device according to claim 11, wherein the cancellation pulse determining
module is further configured to:
when the scheduling information changes, redetermine the cancellation pulse sequence
according to updated scheduling information, and send the redetermined cancellation
pulse sequence to each cancellation pulse generation module for updating.
13. The communications device according to any one of claims 8 to 12, wherein the input
signal is a baseband signal from the baseband unit BBU, or a signal obtained after
previous clipping processing.
14. The communications device according to any one of claims 8 to 13, wherein if the communications
device is an RRU, the communications device further comprises:
an upsampling module that is connected to the peak detection module, configured to:
perform upsampling processing on a received input signal, and input a signal obtained
after the upsampling processing to the peak detection module as an input signal of
the peak detection module.
15. The communications device according to any one of claims 8 to 14, wherein if the communications
device is the BBU, the processing module is further configured to:
send the signal obtained after the clipping processing to an RRU for performing upsampling
processing and intermediate frequency clipping processing.